Well I'm going the cheap route and I bought some ace rust stop brand which is comparable
Rustoleum and it says no thinning is recommended but should I but thinner or hardener in or else its prolly gonna take forever to dry

Heres some good advice for you. Before you ever lay a drop of color on your truck, make sure that the body is flawless. No scratches or little dents or anything because black shows everything. As far as the paint gose go with a good automotive paint like PPG, dupont, sherman williams. Believe me youll save youself alot of headachs.

Truth, black will show everything.
When in school, we don't use hardener in paint. I don't think you are even suppose to?
(Correct if wrong) However, we mix 2:1 With reducer.

thin with mineral spirits.. NOT the odorless kind, its a fad in the honda community called the '$50 dollar paint job' cheap but VERY labor intensive, if done right, actually looks decent.